January 15, 2013

Temperature Extremes Are More Frequent Thanks To Global Warming

Measurements around the world indicate that monthly temperature extremes have become more frequent.

A new study from the Potsdam Institute for Climate Impact Research (PIK) and the Compluntense University reveals that on average, there are five times more record-breaking hot months globally than would be expected without long-term global warming.

The study, published in Climate Change, showed that in parts of Europe, Africa and southern Asia the record-breaking number of months has increased by a factor of ten. The team of scientists claims that without human influence on the climate, 80 percent of the observed monthly records would not have occurred.

“The last decade brought unprecedented heat waves; for instance in the US in 2012, in Russia in 2010, in Australia in 2009, and in Europe in 2003,” Dim Coumou says. “Heat extremes are causing many deaths, major forest fires, and harvest losses — societies and ecosystems are not adapted to ever new record-breaking temperatures.”

NASA supplied the monthly temperature data — collected over 131 years at more than 12,000 grid points globally — which was comprehensively analyzed to reveal the increase in record breaking months.

A robust statistical model was developed by the research team to explain the surge in the number of records because of the long-term global warming trend. Particularly steep over the last 40 years, the surge is due to a steep global-warming trend over this period. The researchers superimposed the data on this long-term rise, showing the effect of natural variability, with especially high numbers of heat records during years with El NiÃ±o events. The natural variability does not explain the development of these record events, however.

The study projects that if global warming continues, the number of new monthly records in 30 years will be 12 times higher than without climate change.

“Now this doesn´t mean there will be 12 times more hot summers in Europe than today — it actually is worse," Coumou points out. According to the study, the records set in the 2040s will not just be hot by today's standards.

“To count as new records, they actually have to beat heat records set in the 2020s and 2030s, which will already be hotter than anything we have experienced to date,” explains Coumou. “And this is just the global average — in some continental regions, the increase in new records will be even greater.”

“Statistics alone cannot tell us what the cause of any single heat wave is, but they show a large and systematic increase in the number of heat records due to global warming,” says Stefan Rahmstorf, co-chair of PIK´s research domain Earth System Analysis. “Today, this increase is already so large that by far most monthly heat records are due to climate change. The science is clear that only a small fraction would have occurred naturally.”